Joining unit

ABSTRACT

A joining unit contains a spindle drive in the form of a hollow shaft motor that encloses a spindle. The hollow shaft motor serves to achieve a linear movement of a joining tool for the execution of a joining process. The joining unit contains instruments for the presetting and/or determination of the forces exerted and/or the movement of the joining tool during the joining process.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to International Application Serial No.PCT/EP2006/007029 filed Jul. 18, 2006.

TECHNICAL FIELD

The invention relates to a joining unit according to the main part ofclaim 1.

BACKGROUND

A joining unit of this type is known from DE 203 05 789 U1.

The joining unit described therein contains a spindle drive for thegeneration of a linear movement of a joining tool. The spindle drive isformed by a hollow shaft motor that encloses a spindle.

The hollow shaft motor is embodied as an electric drive and encompassesa stator as well as a rotor which is firmly attached to the spindle. Therotor causes the spindle to execute a rotational movement.

For the generation of the linear movement of the joining tool a plungeris provided that forms the lower surface of a tubular housing inserthaving an interior space through which a portion of the spindle extends.A nut is provided at the upper side of the housing that engages a threadat the lateral surface area of the spindle. Due to this coupling, therotational movement of the spindle is directly converted into alongitudinal movement of the plunger and, therefore, of the joiningtool.

It is an advantage of this joining unit that the conversion of therotational movement of the spindle drive into a linear movement does notrequire any gearing.

Therefore, the joining unit shows a simple and cost-effectiveconstruction.

It is an essential disadvantage of such joining units that thefunctional control thereof is primarily performed via external units.Although in the joining unit itself are provided position sets whichcontrol the time course of the velocity of the joining tool inaccordance with target positions relative to the workpiece to beprocessed it is necessary to perform the activation of the respectiveposition set via an external unit such as for example an SPS control.

Furthermore, using such external units it is known to perform a powercut-off as a protection against damages of the joining tool or of theworkpiece. In a power cut-off of this type an emergency shut-off of thejoining unit is actuated via the external unit if a maximum allowableforce is exceeded that acts on the spindle. Due to the time required forthe processing of the signal in the external unit as well as the timefor signal transmission between the joining unit and the external unitit may be possible that the emergency shut-off is not actuated in timethus resulting in damages of components of the joining unit due toexcessive straining by force.

Moreover, a system in which essential control functions are performed byexternal units is relatively complex and, therefore, difficult to handleby the user.

BRIEF OBJECTS AND SUMMARY OF THE INVENTION

The object underlying the present invention is a joining unit of thetype mentioned in the beginning that not only has a high functionalityand safety of use but also a simple and cost-effective construction.

To achieve this object the features according to claim 1 are provided.Advantageous embodiments and purposeful modifications of the inventionare described in the dependent claims.

The joining unit according to the invention comprises a spindle drive inthe form of a hollow shaft motor that encloses a spindle and whichserves to achieve a linear movement of a joining tool for the executionof a joining process. The joining unit comprises instruments for thepresetting and/or determination of the forces exerted during the joiningprocess and/or the movement of the joining tool.

In the joining unit according to the invention essential functionsrequired for the control and presetting of the joining process areintegrated into the joining unit itself. In particular, the overallcontrol of the time course of the joining process is integrated in thejoining unit itself making it a closed and largely self-sufficientsystem. The joining unit embodied in this manner has a highfunctionality besides a compact construction and is furthermore easilyhandled by an operator.

Because the spindle drive according to the invention is embodied in theform of a hollow shaft motor no gearing is necessary for driving thejoining tool so that the joining unit has a small overall installed sizeand can be fabricated at reasonable costs. Moreover, a drive of thistype can be well controlled and its dynamics are high. In addition, noconstraint as to the rotational speed on the input side is exercisedduring the operation of such a gear-less drive. And, because there is nogear there is the additional advantage of having one less wear part thatwould require maintaining. In general, since a gear always has a certaingear play a higher positioning accuracy can be achieved by using joiningunits that have gear-less drives than by using systems which functionwith gears.

It is particularly advantageous that essential functions for thesequential control and the control of the joining process are integratedinto a controller of the hollow shaft motor that has the form of anelectric drive.

In particular, not merely position sets for presetting the time courseof the joining process can be stored in this controller but rather theposition sets can also be activated in the controller itself so that noexternal units are required for sequential control.

Furthermore, the controller can carry out control functions for themonitoring or recording, respectively, of the joining process wherein inthis case signals of a speed sensor for the determination of the currentrotational position of the spindle and of a force sensor that measuresthe forces acting on the spindle or the joining tool, respectively, areevaluated within the controller.

In particular, for this purpose a force/displacement evaluation can beperformed within the controller for recording and testing the quality ofthe joining process.

Furthermore, a closed-loop force control can be integrated into thecontroller which serves to prevent damages to components of the joiningunits in the case of high force spikes. It is particularly advantageousto perform the closed-loop force control in a manner that in addition toa closed-loop velocity control also the target position that has to beapproached by the joining tool as predetermined in the currentlyactivated position set will be adjusted against the current processingdirection. In this manner, reversing the direction of the joining toolis initiated and, thus, a collision of the joining tool with an obstacleis prevented.

The closed-loop force control is integrated in the controller of theelectric drive so that no external units are required for this purposeand a quick execution of the closed-loop force control is ensured.

In a particularly advantageous embodiment the joining unit comprises alimit stop switch-off that results in a shut-off of the electric drivein the case of unacceptably high forces and thus protects the joiningunit from damages. It is particularly advantageous if the limit stopswitch-off contains the spring bearing of a force sensor wherebyunacceptably high forces can be sensed by deflection of the springbearing. The limit stop switch-off formed in this manner not only has asimple and robust construction but at the same time protects the forcesensor from damages.

In another useful embodiment the joining unit comprises a holding brakeby means of which a secure holding of the spindle in its set position isensured also during a power failure and in the case of a high weight ofthe joining tool.

It is particularly advantageous if the joining unit has a modularconstruction with respect to its mechanical components. In particular,modular entities are formed by the housing that accommodates theelectric drive and the spindle and by the spindles so that the joiningunit can be configured for different strokes of the joining toolswithout any effort.

In general, the joining unit according to the invention can be used forall types of joining processes. The joining unit can be particularlyused for positional joining wherein a part, for example a bearing, isjoined up to a predetermined introduction depth into a receptacle, forexample a bearing seating. Furthermore, the joining unit can be used toperform block joining wherein a part is assembled into a receptacle upto a collar or, in general, up to an arrest.

Moreover, the joining unit can be used in joining processes related totransformation technique, i.e. in so-called joining by shearing andupsetting or by clinching. In such joining processes positiveconnections are formed by means of clinching of at least two joiningparts. The clinching is performed in connection with cutting or forcefitting and subsequent cold upsetting of the joining parts.

In general, the spindle drive according to the invention can also beused for the generation of linear movements of other tools.

Moreover, the joining unit may also be used for orbital riveting orstamping of parts.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following, the invention will be explained with respect to thedrawings in which:

FIG. 1: shows a perspective view of an example of a joining unit;

FIG. 2: shows a schematic representation of the time course of a joiningprocess that is conducted with the joining unit according to FIG. 1;

FIG. 3: represents the operational profile of the joining tool of thejoining unit in the joining process according to FIG. 2;

FIG. 4: shows an example of a force/displacement diagram for a joiningprocess which can be conducted with the joining unit according to FIG.1;

FIG. 5: shows a schematic representation of the components of a limitstop switch-off for the joining unit according to FIG. 1.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

FIG. 1 shows an example of a joining unit 1. The joining unit 1 isintegrated into an axially symmetric housing 2.

A spindle 3 is placed in the interior of the housing 2 the longitudinalaxis of which extends in the axis of symmetry of the housing 2.Preferably, the spindle 3 is embodied as a ball bearing screw or aplanetary roller drive.

Driving of the spindle 3 is performed by means of a hollow shaft motor 4and, thus, without any use of a gear. The hollow shaft motor 4 is in theform of an electric drive. In the present case, the electric drive isembodied as a servo motor. The stator 4a of the electric drive isarranged at the inner wall of the housing 2 and concentrically with thespindle axis. A tubular body 5 is firmly connected with the spindle 3.The tubular body 5 is essentially in the form of a hollow cylinder thelateral surface of which is arranged concentrically with and in apredetermined distance to the spindle 3. At its front face the tubularbody 5 contains a connecting piece 5 a in the form of a flange by meansof which the tubular body 5 is firmly attached to the spindle 3. At itsopposite end along its length the tubular body 5 is rotatably supportedby means of a bearing 6.

The rotor 4 b is mounted on the outer surface of the tubular body 5 inthe form of an assembly of permanent magnets. The rotor 4 b is disposedopposite to the stator 4 a of the electric drive.

Adjoined to the free end along the length of the spindle 3 and extendingcoaxially and firmly connected therewith is a plunger 7 that is guidedin a guide bush 8 which guide bush 8 is supported in the anteriorportion of the housing 2. The anterior end along the length of theplunger 7 protrudes beyond the front face of the housing 2. At this freeend of the plunger 7 a joining tool 9 for performing a joining processis attached.

A rotational movement of the spindle 3 is caused by means of theelectric drive via the tubular body 5. By means of the guide bush 8 thisrotational movement of the spindle 3 is transformed into a displacementmovement of the plunger 7 in the direction of the longitudinal axis ofthe plunger 7 because the guide bush 8 not merely acts as a guide butalso as a torsion protection for the plunger 7. Due to this linearmovement of the plunger 7 the joining tool 9 conducts a correspondingstroke movement for carrying out a joining process.

As can be seen from FIG. 1, a disc-shaped holding brake 10 is providedin the posterior portion of the housing 2. By means of the holding brake10 the spindle is kept securely in its position, especially if theweight of the joining tool 9 is high or if the drive shuts off in thecase of a power failure, respectively.

Adjoined to the rear end of the tubular housing 2 is a housingprojection 11 at which terminals for connecting a controller (not shown)are provided. The controller is a component of the electric drive andserves for the control thereof.

Furthermore, the controller also performs the control of the wholecontrolling unit. For this purpose, signals of a speed sensor integratedinto the housing protrusion are input in the controller. The speedsensor carries out the determination of the current angular position ofthe spindle 3 as well as its rotational speed. In addition, a forcesensor 12 is provided that encloses the plunger 7 and the signals ofwhich are also input in the controller. By means of the force sensor 12the forces acting on the plunger 7 and, thus, on the joining tool 9 orthe spindle 3, respectively, are determined. The force sensor maycontain strain gauges or piezo sensors as the sensor elements.

The control of the time course of the joining process to be carried outby means of the joining unit 1 is performed in the controller. Positionsets are stored as operation parameters for process control within thecontroller and individual position sets are activated one after theother in the controller for presetting the joining process. Eachposition set contains the target position to be approached by thejoining tool 9 as well as the velocity of the joining tool 9 by whichthe target position is approached.

An example for a joining process of this type is illustrated in FIGS. 2and 3. FIG. 2 represents the different phases of the joining processthat are referred to as a to f. FIG. 3 shows the different velocities ofthe joining tool 9 for these phases.

FIG. 1 shows individually for each of the phases a to f of the joiningprocess the position and optionally also the movement of the joiningunit 1 containing the joining tool 9 relative to a mount 13 that servesfor the accommodation of the workpiece 14 to be processed.

The joining process starts from an initial position of the joining unit1 (phase a) in which the joining tool 9 is not moved and is disposed ata distance from the mount 13.

During the following phase b a position set 0 is activated so that thejoining tool 9 is advanced to the mount 13 with a first velocity asdefined in the position set and without the workpiece 14 as demonstratedin FIGS. 2, 3. This phase is designated as idle stroke 1.

In phase c (joining 1) a joining process is simulated wherein thejoining tool 9 is inserted in the mount 13 with a second velocity aspredetermined in position set 1.

This is followed by phase d (idle stroke 2) in which the joining tool 9is moved with a velocity as defined in position set 2.

During phase e (joining 2) the joining of the workpiece 14 is carriedout with the velocity as defined in position set 3.

A return stroke is subsequently performed in phase f with a velocity asdefined in position set 4 during which the joining tool 9 is removedagain from the mount.

Furthermore, also a force/displacement evaluation is performed withinthe controller. In this case, by evaluating the signals of the speedsensor and of the force sensor the force path is determined inaccordance with the path traveled by the joining tool 9. Thecorresponding data can be output from the controller to an external unitfor the visualization of this force path. An example of such a diagramis shown in FIG. 4. Such force/displacement diagrams serve to monitorand control the quality of the joining process. In the example accordingto FIG. 4 two ranges of tolerance T₁, T₂ are given. An accurate joiningprocess is obtained if the corresponding force in specific path areasfalls within the tolerance ranges.

Moreover, a closed-loop force control is integrated into the controller.Due to this closed-loop force control the velocity and also the currenttarget position in the current position set are altered if the forcemeasured by the force sensor 12 exceeds a predetermined threshold value.In this case it will be particularly advantageous to alter the targetposition against the current operating direction of the joining tool 9.The velocity change and the target position change are performed in arange that has been specifically predetermined by the user for therespective application. A force exceeding the threshold value is forexample encountered if the joining tool 9 collides with an obstacle.Since the target position is changed against the processing direction ofthe joining tool 9 a reversal of the joining tool 9 is achieved by meansof the closed-loop force control whereby the obstacle is avoided anddamages to components of the joining unit 1 can be prevented, i.e. anoverload protection is achieved for the joining unit 1.

FIG. 5 shows an example of a limit stop switch-off 15 that can beintegrated into the joining unit 1 according to FIG. 1. FIG. 5represents a force sensor 12 that encloses the spindle 3 of the joiningunit 1. Alternatively, as shown in FIG. 1, the force sensor can enclosethe plunger 7.

The force sensor 12 according to FIG. 5 is resiliently supported bymeans of a spring bearing. The spring bearing consists of two springassemblies 16 a, b extending in axial direction of the spindle 3 on bothsides of the force sensor 12. The spring assemblies 16 a, b each containsprings 18 a, b supported in a chamber 17 a, b wherein the bottom 19 a,b of each chamber 17 a, b is slidable against the upper portion of thechamber 17 a, b against the spring forces.

The springs 18 a, b of each spring assembly 16 a, b are pretensionedwith a pretension force wherein each pretension force corresponds to alimit value. The limit value G is defined as

G=N+T

wherein N is the nominal joining force and T is a positive tolerancevalue.

Assigned to each of the spring assemblies 16 a, b are switches 20 a, bwherein in the present case the switches 20 a, b are embodied asopeners. The signals from the switches 20 a, b are transferred to aninverter 21 via which they are input in the controller.

If the force acting on the force sensor 12 exceeds the limit value thesprings 18 a, b of the first or second spring assembly 16 a, b aredeflected in dependence on the direction of the force so that the switch20 a or b, respectively, of the respective spring assembly 16 a or b isactuated. This signal is input to the controller that executes anemergency stop of the joining unit 1. Due to this limit stop switch-offthe joining unit 1 is protected from force spikes that exceed thenominal joining force.

By means of the limit stop switch-off 15 especially the force sensor 12can be protected from overload. If the spindle is in the form of a ballbearing screw, this can also be protected from overload.

1. A joining unit containing a spindle drive in the form of a hollowshaft motor that encloses a spindle to achieve a linear movement of ajoining tool for the execution of a joining process wherein said joiningunit contains instruments for the presetting and/or determination of theforces exerted during the joining process and/or the movement of thejoining tool.
 2. A joining unit having a spindle drive in the form of ahollow shaft motor enclosing a spindle to achieve a linear movement of ajoining tool for the execution of a joining process wherein said joiningunit contains a force sensor which is formed by at least one piezosensor.
 3. The joining unit according to claim 1 wherein the hollowshaft motor contains an electric drive having a controller for thecontrol thereof wherein in said controller are integrated at least apart of the instruments for the presetting and/or determination of theforces exerted during the joining process and/or the movement of thejoining tool.
 4. The joining unit according to claim 1, wherein saidjoining unit contains a speed sensor for the determination of thecurrent rotational position of the spindle driven by the electric driveand wherein the force sensor serves for the determination of the forcesacting on the joining tool.
 5. The joining unit according to claim 3,wherein position sets are stored in the controller where they can beactivated for the presetting of joining processes.
 6. The joining unitaccording to claim 4, wherein a force/displacement evaluation of thejoining process is performed in the controller in dependence on thesignals of the speed sensor and the force sensor.
 7. The joining unitaccording to claim 3, wherein a closed-loop control unit is integratedin the controller for performing a closed-loop force control.
 8. Thejoining unit according to claim 7 wherein during closed-loop forcecontrol the target position predetermined in the currently activatedposition set is changed if the force as determined by the force sensorexceeds a predetermined threshold value.
 9. The joining unit accordingto claim 8 wherein during closed-loop force control the change of thetarget position is carried out against the operating direction of thejoining tool.
 10. The joining unit according to claim 8, wherein duringclosed-loop force control the velocity of the joining tool is changed independence on the force determined by the force sensor.
 11. The joiningunit according to claim 1, wherein said joining unit contains a limitstop switch-off for performing an emergency stop of the electric drive.12. The joining unit according to claim 11 wherein the limit stopswitch-off is actuated if the force acting on the joining tool exceeds alimit value.
 13. The joining unit according to claim 12 wherein for thepresetting of the limit value a spring bearing is provided for the forcesensor which is formed by two spring assemblies, one of said springassemblies being arranged in longitudinal direction of the spindle oneach side of the force sensor wherein the pretension of the springs ofthe spring assemblies corresponds to said limit value.
 14. The joiningunit according to claim 12, wherein the limit value corresponds to thesum of the nominal joining force and a tolerance value.
 15. The joiningunit according to claim 13, wherein a switch is assigned to each springassembly wherein each switch generates a switch signal that is evaluatedin the controller with respect to the actuation of the emergency stop ifthe limit value for any of the spring assemblies is exceeded.
 16. Thejoining unit according to claim 1, wherein said joining unit contains aholding brake that acts on the spindle.
 17. The joining unit accordingto claim 1, wherein the mechanical components thereof have a modularconstruction so that they can be adapted to different strokes of thejoining tool to be performed during the joining process.
 18. The joiningunit according to claim 3, wherein the electric drive forming the hollowshaft motor contains a stator supported in a housing as well as a rotormounted on a tubular body that is firmly attached to and enclosing thespindle.
 19. The joining unit according to claim 18 wherein adjoined tothe spindle is a plunger extending coaxially with the spindle at thefree end of which the joining tool can be mounted and furthercharacterized in that the plunger is guided in a guide bush supported inthe housing whereby the rotational movement of the spindle caused by theelectric motor is transformed into a longitudinal movement of theplunger.
 20. The joining unit according to claim 19 wherein thecomponents having a modular construction are formed by the spindle andthe housing.
 21. The joining unit according to claim 2 wherein thehollow shaft motor contains an electric drive having a controller forthe control thereof wherein in said controller are integrated at least apart of the instruments for the presetting and/or determination of theforces exerted during the joining process and/or the movement of thejoining tool.
 22. The joining unit according to claim 2 wherein saidjoining unit contains a speed sensor for the determination of thecurrent rotational position of the spindle driven by the electric driveand wherein the force sensor serves for the determination of the forcesacting on the joining tool.
 23. The joining unit according to claim 21wherein position sets are stored in the controller where they can beactivated for the presetting of joining processes.
 24. The joining unitaccording to claim 22 wherein a force/displacement evaluation of thejoining process is performed in the controller in dependence on thesignals of the speed sensor and the force sensor.
 25. The joining unitaccording to claim 21 wherein a closed-loop control unit is integratedin the controller for performing a closed-loop force control.
 26. Thejoining unit according to claim 25 wherein during closed-loop forcecontrol the target position predetermined in the currently activatedposition set is changed if the force as determined by the force sensorexceeds a predetermined threshold value.
 27. The joining unit accordingto claim 26 wherein during closed-loop force control the change of thetarget position is carried out against the operating direction of thejoining tool.
 28. The joining unit according to claim 26 wherein duringclosed-loop force control the velocity of the joining tool is changed independence on the force determined by the force sensor.
 29. The joiningunit according to claim 2 wherein said joining unit contains a limitstop switch-off for performing an emergency stop of the electric drive.30. The joining unit according to claim 29 wherein the limit stopswitch-off is actuated if the force acting on the joining tool exceeds alimit value.
 31. The joining unit according to claim 30 wherein for thepresetting of the limit value a spring bearing is provided for the forcesensor which is formed by two spring assemblies arranged in longitudinaldirection of the spindle, one said spring assembly being on each side ofthe force sensor wherein the pretension of the springs of the springassemblies corresponds to said limit value.
 32. The joining unitaccording to claim 30 wherein the limit value corresponds to the sum ofthe nominal joining force and a tolerance value.
 33. The joining unitaccording to claim 31 wherein a switch is assigned to each springassembly wherein each switch generates a switch signal that is evaluatedin the controller with respect to the actuation of the emergency stop ifthe limit value for any of the spring assemblies is exceeded.
 34. Thejoining unit according to claim 2 wherein said joining unit contains aholding brake that acts on the spindle.
 35. The joining unit accordingto claim 2 wherein the mechanical components thereof have a modularconstruction so that they can be adapted to different strokes of thejoining tool (9) to be performed during the joining process.
 36. Thejoining unit according to claim 21 characterized in that the electricdrive forming the hollow shaft motor contains a stator supported in ahousing as well as a rotor mounted on a tubular body that is firmlyattached to and enclosing the spindle.
 37. The joining unit according toclaim 36 wherein adjoined to the spindle is a plunger extendingcoaxially with the spindle at the free end of which the joining tool canbe mounted and wherein the plunger is guided in a guide bush supportedin the housing whereby the rotational movement of the spindle caused bythe electric motor is transformed into a longitudinal movement of theplunger.
 38. The joining unit according to claim 37 wherein thecomponents having a modular construction are formed by the spindle andthe housing.